In almost all fields of information technology, the data rates increase continuously. The transfer of data as electrical signals via copper wires comes to physical limits. Much higher data rates can be transferred as optical signals via fibre optic cables or other optical waveguides.
Optical signals can be switched by means of electro-optical switches. However, for many applications all-optical switches are required and/or advantageous. In an all-optical switch, a first signal carrying information encoded in modulation of the intensity or power is switched by a second optical signal. When the intensity of the second signal is higher, the first signal is transmitted and when the intensity of the second signal is lower, the first signal is blocked, or vice versa.
U.S. patent publication number 2004/0033009 A1 describes a bistable switch in a photonic crystal wherein two waveguides are arranged perpendicular to each other. At the intersection each waveguide comprises a number of rods in a line. The central rod belonging to both waveguides is larger and thereby forms a defect. The rods and the central defect form a cavity with a resonance frequency. The resonance frequency depends on the refractive indices of the materials forming the cavity. One of the materials of the cavity is a Kerr material, the refractive index of which depends on the intensity of light or the amplitude of its electric field. Via the intensity of light in one of the waveguides, the resonance frequency and hence the transparency of the cavity for light in the other waveguide is modulated.
For many applications, the switching behavior of the conventional switch of the above-cited U.S. patent publication may be insufficient. In particular, a better optical trans-conductance (i.e., a batter change of transparency in one of the waveguides for a given change of intensity in the other waveguide) is desired.